In many applications of hydraulic pump assemblies it is important that means be provided to limit the fluid pressure generated by the pump to prevent damage to the hydraulic ram cylinders connected to the hydraulic pump or damage to other structural components supported by the hydraulic rams. For example, in the case of a conventional bottle jack, it is important that the hydraulic fluid pressure supplied by the hydraulic fluid pump to the jack ram cylinder not exceed the capacity of the ram cylinder. In the case of a portable hydraulic crane of the type including a boom supported by a hydraulic ram it is important that the boom should not be used to lift objects which will overload the crane and that the hydraulic ram not be permitted to apply an upward force on the boom which will structually overload the crane. In some prior art portable cranes the base of the hydraulic assembly is provided with a high pressure fluid relief passage extending from the hydraulic pump to the fluid reservoir to relieve fluid from the pump to the reservoir in the event the fluid pressure generated in the pump exceeds a selected maximum pressure. The fluid relief passage in the base includes a valve seat, and a ball held in engagement with the valve seat by a compression spring. The compression spring applies sufficient force on the ball that the ball engages the valve seat and precludes fluid flow unless the fluid pressure generated by the pump reaches a maximum selected value.